Throughout this application various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
The inventors acknowledge and appreciate the assistance of Dr. Elise Sudbeck.
Design of potent inhibitors of human immunodeficiency virus (HIV-1) reverse transcriptase (RT), an enzyme responsible for the reverse transcription of the retroviral RNA to proviral DNA, has been a focal point in translational AIDS research efforts (Greene, W. C., New England Journal of Medicine, 1991, 324, 308-317; Mitsuya, H. et al., Science, 1990, 249, 1533-1544; De Clercq, E., J. Acquired Immune Defic. Syndr. Res. Human. Retrovirus, 1992, 8, 119-134). Promising inhibitors include nonnucleoside inhibitors (NNI), which bind to a specific allosteric site of HIV-1 RT near the polymerase site and interfere with reverse transcription by altering either the conformation or mobility of RT, thereby leading to noncompetitive inhibition of the enzyme (Kohlstaedt, L. A. et al., Science, 1992, 256, 1783-1790).
NNI of HIV-1 RT include the following:
(a) 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymines (HEPT; Tanaka, H. et al., J. Med. Chem., 1991, 34, 349-357; Pontikis, R. et al., J. Med. Chem., 1997, 40, 1845-1854;
Danel, K., et al., J. Med. Chem., 1996, 39, 2427-2431; Baba, M., et al., Antiviral Res, 1992, 17, 245-264);
(b) tetrahydroimidazobenzodiazepinethiones (TIBO; Pauwels, R. et al., Nature, 1990, 343, 470-474);
(c) bis(heteroaryl)piperazines (BHAP; Romero, D. L. et al., J. Med. Chem., 1993, 36, 1505-1508);
(d) dihydroalkoxybenzyloxopyrimidine (DABO; Danel, K. et al., Acta Chemica Scandinavica, 1997, 51, 426-430; Mai, A. et al., J. Med. Chem., 1997, 40, 1447-1454);
e) 2xe2x80x2-5xe2x80x2-bis-O-(tertbutyldimethylsilyl)-3xe2x80x2-spiro-5xe2x80x3-(4xe2x80x3-amino-1xe2x80x3,2xe2x80x3-oxathiole-2xe2x80x3,2xe2x80x3-dioxide) pyrimidines (TSAO; Balzarini, J. et al., Proc. Natl. Acad. Sci. U S A, 1992, 89, 4392-4396); and
(f) phenethylthiazolylthiourea (PETT) derivatives (Bell, F. W. et al., J. Med. Chem., 1995, 38, 4929-4936; Cantrell, A. S. et al., J. Med. Chem., 1996, 39, 4261-4274).
Current protein structure-based drug design efforts rely heavily on crystal structure information of the target binding site. A number of crystal structures of RT complexed with NNIs (including xcex1-APA, TIBO, Nevirapine, BHAP and HEPT derivatives) have been reported, and such structural information provides the basis for further derivatization of NNI aimed at maximizing binding affinity to RT. However, the number of available crystal structures of RT NNI complexes is limited, and no structural information has been reported for RT-PETT complexes or RT-DABO complexes. Given the lack of structural information, researchers must rely on other design procedures for preparing active PETT and DABO derivatives. One of the first reported strategies for systematic synthesis of PETT derivatives was the analysis of structure-activity relationships independent of the structural properties of RT and led to the development of some PETT derivatives with significant anti-HIV activity (Bell, F. W. et al., J. Med. Chem., 1995, 38, 4929-4936; Cantrell, A. S. et al., J. Med. Chem., 1996, 39, 4261-4274). The inclusion of structural information in the drug design process should lead to more efficient identification of promising RT inhibitors.
Although the crystal structure of an RT-NNI complex can be used to provide useful information for the design of a different type of NNI, its application is limited. For example, an analysis of the RT-APA (xcex1-anilinophenylacetamide) complex structure would not predict that the chemically dissimilar inhibitor TNK (6-benzyl-1-benzyloxymethyl uracil) could bind in the same region. The RT-APA structure reveals that there would not be enough room in the APA binding site for the 1-benzyloxymethyl group of TNK (Hopkins, A. L. et al., J. Med. Chem., 1996, 39, 1589-1600). Nevertheless TNK is known to bind in this region as evidenced by the crystal structure of RT-TNK which shows that RT residues can adjust to accommodate the 1-benzyloxymethyl group. Conversely, an analysis of the RT-TNK complex would not predict favorable binding of APA in the TNK binding site. The structure does not show how residue E138 can move to accommodate the 2-acetyl group of the xcex1-APA inhibitor.
Thus, any NNI binding pocket model based on an individual RT-NNI crystal structure would have limited potential for predicting the binding of new, chemically distinct inhibitors. To overcome this problem, the invention disclosed herein uses the NNI binding site coordinates of multiple, varied RT-NNI structures to generate a composite molecular surface. A specific embodiment of the invention is a composite molecular surface or binding pocket generated from nine distinct RT-NNI complexes, and reveals a larger than presumed NNI binding pocket not shown or predicted by any of the individual structures alone (FIG. 2A). This novel composite binding pocket, together with a computer docking procedure and a structure-based semi-empirical score function, provides a guide to predict the energetically favorable position of novel PETT, DABO, and HEPT derivatives, as well as other novel compounds, in the NNI binding site of RT.
The invention further provides a number of computational tools which set forth a cogent explanation for the previously unexplained and not understood relative activity differences among NNIs, including PETT, DABO, and HEPT derivatives, and reveals several potential ligand derivatization sites for generating new active derivatives. Disclosed herein is the structure-based design of novel HEPT derivatives and the design and testing of non-cytotoxic PETT and DABO derivatives which abrogate HIV replication in human peripheral blood mononuclear cells at nanomolar concentrations with an unprecedented selectivity index of  greater than 105.
One procedure useful in structure-based rational drug design is docking (reviewed in Blaney, J. M. and Dixon, J. S., Perspectives in Drug Discovery and Design, 1993, 1, 301). Docking provides a means for using computational tools and available structural data on macromolecules to obtain new information about binding sites and molecular interactions. Docking is the placement of a putative ligand in an appropriate configuration for interacting with a receptor. Docking can be accomplished by geometric matching of a ligand and its receptor, or by minimizing the energy of interaction. Geometric matching is faster and can be based on descriptors or on fragments.
Structure-based drug design efforts often encounter difficulties in obtaining the crystal structure of the target and predicting the binding modes for new compounds. The difficulties in translating the structural information gained from X-ray crystallography into a useful guide for drug synthesis calls for continued effort in the development of computational tools. While qualitative assessments of RT-inhibitor complexes provide helpful information, systematic quantitative prediction of inhibitory activity of new compounds based on structural information remains a challenge.
There is a need for more complete information on the structure and flexibility of the NNI binding pocket and for an improved model of the binding pocket to serve as a basis for rational drug design. In addition, there is a need for more effective inhibitors of reverse transcriptase, particularly HIV-1 reverse transcriptase.
The invention disclosed herein addresses these needs by providing a model for the three-dimensional structure of the RT-NNI binding pocket based on the available backbone structure of RT-DNA complex and full structure of RT complexed with several NNI compounds. Structural information from multiple RT-NNI complexes was combined to provide a suitable working model. In one embodiment, the NNI binding site coordinates of nine RT-NNI structures is used to generate a composite molecular surface revealing a larger than presumed NNI binding pocket. This pocket, together with docking and a structure-based semi-empirical score function, can be used as a guide for the synthesis and analyses of structure-activity relationships for new NNI of RT, including new derivatives of HEPT, DABO, and PETT, as well as novel compounds having little or no relationship to known NNIs. The practical utility of this novel composite model is illustrated and validated by the observed superior potency of new PETT and S-DABO derivatives as anti-HIV agents, described herein.
The invention provides novel compounds which inhibit reverse transcriptase (RT) and which inhibit replication of a retrovirus, such as human immunodeficiency virus-1 (HIV-1). In one embodiment, the novel compounds of the invention are analogs or derivatives of phenethylthiazolylthiourea (PETT), dihydroalkoxybenzyloxopyrimidine (DABO) or 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT). Alternatively, the novel compounds of ID the invention bind the NNI binding pocket, but are not related to any known NNI. Specific compounds of the invention are described more fully in the Detailed Description and in the Examples below.
The invention additionally provides compositions and methods for inhibiting reverse transcriptase activity of a retrovirus, such as HIV-1, by contacting the RT binding site of the retrovirus with a compound of the invention. The methods of the invention are useful for inhibiting replication of a retrovirus, such as HIV-1 and include treating a retroviral infection in a subject, such as an HIV-1 infection, by administering a compound or composition of the invention, for example, in a pharmaceutical composition.
The invention further provides a composite ligand binding pocket constructed by superimposing multiple structures of ligand-binding site complexes. Preferably, the composite binding pocket is constructed by superimposing the structures of at least one each of the following NNI complexed with RT: a compound, analog or derivative of HEPT or MKC; TNK, APA, Nevipapine, and TIBO. In one embodiment, the composite ligand binding pocket is an HIV-1 reverse-transcriptase (RT) nonnucleoside inhibitor (NNI) binding pocket constructed by superimposing nine structures of NNI-RT complexes, preferably having the coordinates set forth in Table 9.
Using the novel composite binding pocket of the invention, compounds that bind to the NNI binding site of reverse transcriptase can be identified and/or screened. For example, a useful inhibitor is identified by analyzing the fit of a candidate compound to the composite binding pocket is analyzed. In one embodiment, the comparing comprises analyzing the molecular surface of the composite binding pocket. The extent of contact between the molecular surface of the compound and the molecular surface of the binding pocket can be visualized, and any gap space between the compound and the composite binding pocket can be determined and quantified. The candidate inhibitory compound can be docked in the composite binding pocket, and its binding characteristics analyzed. For example, an estimate of the inhibition constant for the docked compound can be calculated. The value of the inhibition constant is inversely related to the affinity of the candidate compound for the binding pocket.
Using information provided by the composite binding pocket of the invention, novel inhibitors of reverse transcriptase can be designed and screened. Using molecular modeling techniques, a compound can be docked into an RT-NNI binding pocket, and the complex analyzed for its binding characteristics. Gap space or regions that do not demonstrate optimum close contacts between the compound and the binding pocket are identified, permitting the compound to be modified to better occupy the site. In such a method, novel inhibitors of reverse transcriptase are designed and screened.
Also provided by the invention are inhibitors of reverse transcriptase identified or designed by analyzing the compound""s structural fit to the binding pocket. Potent inhibitors designed and confirmed using the composite binding pocket of the invention include analogs and derivatives of known NNI, such as phenethylthiazolylthiourea (PETT) analogs, dihydroalkoxybenzyloxopyrimidine (DABO) analogs, and 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) analogs.
The compounds of the invention may be combined with carriers and/or agents to enhance delivery to sites of viral infection, such as targeting antibodies, cytokines, or ligands. The compounds may include chemical modifications to enhance entry into cells, or may be encapsulated in various known delivery systems.